Electric valve translating circuit



l... F. LITI'WIN ELECTRIC VALVE TRANSLATING CIRCUIT Filed July 11, 1942 Patented Dec. 7, 1943 UNITED lSTATES PATENT OFFICE ELECTRIC VALVE TRANSLATING CIRCUIT Leo F. Littwin, Chicago, Ill.

Application July 11, 1942, Serial No. 450,645

(Cl. Z50-27) 11 Claims.

. tions of a machine tool.

In machine tools having a reciprocating traveling work table anda tool head operable transversely with respect to the work table, it has been found desirable to provide means for automatically advancing the tool head each time that the work table reciprocates or each time that the work table moves in either direction. Heretofore, this has been accomplished by an apparatus utilizing an electric circuit which was closed each time that the work table completed its travel or its cycle of operation, and was opened by electric contact devices and relays as the cutting head or tool head was advanced a predetermined amount. Such circuits employed electromagnetic relays and a series of electric contacts spaced along the `way or the path of travel of the tool head. It was found that the variations in the times of operation of the relays was suiciently great to introduce deleterious inaccuracies n the operation of the machine tools, and that furthermore it was di'icult to maintain the contacts clean so as to prevent delayed operation ldue to variations in contact resistance. In accordance with my invention a tool head is advanced at a certain constant rate of travel, and the distance which the tool head is advanced is determined by controlling the time interval during which the tool head travels without the use of relays or contacts. This is accomplished by utilizing an electric valve translating circuit which may be controlled so as to supply electric power for predetermined periods of time thereby to control the distance through which a tool head is advanced at a certain constant rate of travel.

`It is therefore an object of my invention to prof` vide an improved electric valve translating circuit for controlling the operation of a machine tool which will overcome the above mentioned disadvantages.

",It is another object of .my invention to provide an improved electric valve circuit for selectively predetermining the time interval of operation of a device, irrespective of the variations in the intervals between successive operations.

A still further object of my invention is to provide an improved control circuit for an electric valve translating lapparatus which will-be reliable in operationand simple and economical to manufacture. Y v, Y

`Other and further objects of my invention will become more readily apparent by reference to the ,following description taken in connection with the accompanying drawing wherein,

Figure lis a perspective View of the essential parts of a machine tool to which the present invention is applied; and

Figure 2 is a circuit diagram of the electric valve translating apparatus and the control circuit therefor which embodies the present invention.

Referring more particularly to Figure 1, there are shown certain essential elements of a machine tool, and these include a supporting frame 5 upon which a work table 6 is arranged to travel on horizontal ways. The work table 6 is actuated by such mechanism as is common in the art and which may be variable in speed vand which can be controlled so as to determine the length of travel of the Work table. Supported toward the rear of the base or frame 5 are two vertical co1- umns I and 8 provided with suitable slides or ways to guide the travel of a tool head support 9, which in yturn is provided with suitable slides or ways in which a tool head I I operates. Thus, by means of the vertical slides or ways formed in the columns "I and A8, the tool head II may be positioned at the desired elevation with respect to the work table 6. In the gure, tool head II is shown as being a grinding wheel provided with a shield and lubricating tube, but it is to be understood that this tool head may com-r prise anyother cutting or finishing tool. n In operation, the work table 6 moves back and forth between certain limits which may be predetermined by a pair of adjustable limit stops I2 and I3 suitably supported beneath the front edge of the work table 6. Theselimit stops actuate a pair of switch levers I4 and I5 Awhich are connected to some means for controlling the reversal of the direction of operation of the work table 6. As the4 stock on the work table 6 is moved relative to the cutting head I I, it is desired to automatically move the tool Yhead II across the stock by small increments of distance. This may be accomplished by any suitable means operating at a constant rate of speed such as a hydraulic piston I 6, shown in dotted lines, which is supplied through a pipe I'I and a valve I8. The valve I8 is opened and closed by a solenoid I9. The solenoid I9 is energized by an electric circuit which is controlled by a switch 2| actuated by suitable switch actuating toggle means 22 connected to the vlimit switch levers I 4 and I5; In the `arrangement shown, each actuation of either of the levers I4 or I5 produces actuation of the toggle 22 thereby closing the switch 2| for a brief time interval.

` Referring more particularly to Figure 2, there is shown an electric valve translating apparatus which is energized from a suitable source of alternating current by means of the conductors 23 and 24. Connected between the conductors 23 and 24 in series with the solenoid I9 are a pair of reversely connected controlled electric valves 25 and -26 which controll the supply of energyV toV thejsolenoid I9 thereby controlling the operation of the valve I8. The valves 25 and 26 may comprise any one of a number of types of controlled electric valves well known in the art, but for purposes of illustration there is shown a form of electric valve having an anode,

conductor I, the secondary winding 31 of the transformer 21, and through the secondary winding 45 of the transformer 26 to the control electrode. The control electrode of the valve 26 is connected to a control circuit which may be traced through the secondary winding 46 of the transformer 28, and the secondary winding 38 of the transformer 21 to the cathode of the valve.

In order to determine the periodsfduring which the voltages supplied by the transformers 21 and 28 are effective in the control circuits of valves 25 and 26, there is provided a half-wave rectifier 36 connected so as to charge a capacitor 52 may have control characteristics which requirev certain relations between the control potentials applied, but for the purpose of simplification, in

the explanation of the circuit, it will be assumed that the valves herein used have control characteristicssuch that they will become conductive whenever the control electrode is at zero or slightly positive potential with respect to the cathode. Whenever the valves 25 and 26 supply energy to the solenoid I9, the valve I8 permits uid to be supplied to the hydraulic cylinder I6 thereby to advance the tool head II at a certain constant rate. The time interval during which the valve I8 is open which determines the'distance which the tool head will advance, is in turn determined by the length of time of conductivity of thevalves 25 and 26.

In order to provide definite periods of conductivity for the valves 25 and 26, there is provided a-control circuit which includes a transformer 21 which supplies potential tending to maintain the valves non-conductive and Aa transformer 28 which suppliesV potential of such sign and magnitude as to overcome the effect of the potential supplied by the transformer 21. The transformer 21 is provided with a primary winding Y29 directly connected'between the conductors 23 and 24. The transformer 21 is provided with a plurality of secondary windings,of which windings 3l, 32, 33, 34 supply current for heating the cathodes'of Ythe electric valves 25 and 26 landalso of auxiliary valve 35 and a rectifier valve 36. The secondary windings 31 and 38 of the transformer 21- are connected to the control electrodes of the valves 25 and 26, respectively. A capacitor 4I is connected in parallel with the transformer winding 39 andl a resistor 42 which is in series with this transformer-Wind.- ing. The primary winding 39, theseries resistor 42, Vand the capacitor 4| in parallelthereto are connected in series with a resistor 43; and these circuit elements'are in parallel with the solenoid I9. The juncture between the resistorV 42 and the primary winding is connected by means of a conductor 44 through the switch 2l to the electric conductor 23. The transformer 25 is provided with a pair of secondary windings 45 and 46 .which are connected in series with the secondary windings31land 38 respectively of the transformer 21.Y

As is customary, in order to improve the control `of the control electrodes of the valves 25 Vand26,each ofthe control electrodes thereof LTI which is connected in parallel with a pair of re- Ysistors or impedances 53 and 54. The common juncture between the resistor 54 and the capacioperating on a resistor 56 connected in series wtih another resistor 51, the end terminal of whichY is connected through a conductor 58 to the common juncture between the resistor 42V and the solenoid I 9. During the time that the valves 25 and 26 are non-conductive, the alternating current potential supplied across the conductors 23 and 24 is suncient to cause the rectifier 36 to be conductive thereby to charge the capacitor 52. The manner in which this potential becomes effective can best be understood by tracing 'the following circuit from the conductor 23 to the cathode of the rectifier 36, from the anode of the rectifier 36 to the parallel circuit comprising the capacitor 52 and the serially connected resistors 53 and 54, through the adjustable contact 55, a portion of the resistor 55, the resistor 51, the conductor 58, the resistor 42, the solenoid i9, to the conductor 24. When.- ever electric valves 25 and 26 are conductive, the potential appearing across the rectifier 36 is insufficient to maintain conductivity of the rectier so that it no longer supplies energy to charge the capacitor Y52. The capacitor 52 thereupon discharges through the resistors 53 and 54 thereby building up a potential across these resistors. The resistor 54 is connected between the control electrode of an auxiliary valve 35 and the cathode thereof by means of the. adjustable contact 55 and the resistor 56. The resistors 56 and 51 are connected across the secondary winding 33 of the transformer 21, which winding is connected to the cathode of the auxiliary valve 35.

The auxiliary valve 35 is effectively connected across the primary winding 39 of the transformer 28 since the conductor 53 from the cathode of valve 35 is connected through resistor 42 to one terminal of the winding 39. 'I'he anode of the auxiliary valve 35 is connected through a conductor 59 to the other side of the primary winding 39. During the time that the capacitor` 52 isbeing charged by the rectifier 36, the voltage appearing across the resistor 54 is of such sign and magnitude as to maintain non-conductive the electric valve 35. During this time also there is no potential appearing across the primary winding 39 of the transformer 28. As s oon as electric valves 25 and 26 become conductive, a potential appears across the primary winding 39 of the transformer 38 because of the. current owing through the solenoid I9. Thus, at'this instant potential is supplied between the anode and cathode of the electric valve 35. Also at the instantV of conductivity of the valves 25 and 26, the rectifier 36 ceases to Yfunction so that the capacitor 52 discharges through the resistors53 and 54 thereby reversing the polarity of the potential appearing across `the resistor 54. When this potential reaches a critical amount, the control electrode of the auxiliary valve 35 permits the valve to become conductive. The particular instant at which this auxiliary valve becomes conductive may be controlled by adjustment of the position of the contact 55 on the resistor 56 since it will be apparent that a certain amount of alternating current potential is present in the circuit of the control electrode.

The operation of the electric valve translating apparatus will be more readily understood by reference to the following description of the operation thereof. The electric valves 25 and 26 are normally maintained non-conductive by the bias potential supplied by the Vsecondary windings 3l and 33 of the transformer 2l, the primary winding of whichis directly connected between the conductors 23 and 24. During the time that the main valves 25 and 25 are nonconductive, the alternating current potential appearing across the electric rectier 35 is suicient to cause this to be conductive thereby supplying energy to charge the capacitor 52. It will be remembered that the travel of the work table 6 of the machine shown in Figure 1 causes the l adjustable limit stop members 'l2 and `I3 to actuate the limit switch members I4 and l5 so that at the end of each travel of the table 5 y rent through the solenoid I9 so as to produce A no appreciable eiiect thereon. Thus during the time that the switch 2| is closed potential is supplied to the primary winding 39 so that alternating current potential appears in the secondary windings 45 and 46 which will'be of such'sign and magnitude as to render ineffective the negative biasing potential supplied by the secondary windings 3l and 38 which are connected in the control circuits for electric valves 25 and 25. Thus the control electrodes of the main valves 25 and 26 are subjected to a specific potential which positively insures the conductivity of at least one of these valves. Even though the switch 2| were closed for such a short time interval as to 'permt only one of the valves to become conductive, the other valve thereupon will also become conductive because as soon `as any valve is conductive, a potential is developed across the solenoid I9. A portion of this potential appears across the primary winding 39 of the transformer 38 so that potentials are app-lied by the secondaryy windings 45 and 45 to insure the continuation of the conductivity of these valves. i

' At the time of the initiation of conductivity of the electric valves 25 `and 25, the rectier 33 stops supplying energy to the capacitor 52 so that the capacitor discharges through the re` sistors 53 and 54. lSince the current flowing through the solenoid I5 develops a potential across the transformer winding 39, an alterhating `potential now appears across the auxiliary valve 35. By adjustment of the contact 55 on the resistor 5S, there is predetermined a time constantwhich determines theperiod of The other y;

conductivity of the valves 25 and 25. As soon as the potential developed across the resistor 54 is sufficient to permit the auxiliary valve 35 to become'conductive, the primary winding 39 of the transformer 28 is then shunted by a relatively low impedance so that the potential appearing across the primary winding 39 is insufficient to permit the secondary windings 45 and 46 to supply suihcient voltage to maintain the conductivity of the electric valves 25 and 23. Since the potentials supplied by the transformer windings 45 and 46 are insuiicient, the negative bias potentials supplied by the secondary windings 31 and 38 of the transformer 21 now cause the electric valves 25 and 26 to become non-conductive. As soon as the valves 25 and 25 become non-conductive, there again appears a potential across the rectier 35 sufficient to cause it to become conductive thereby charging the capacitor 52 so that the circuit is in readiness for another cycle of operation.

From the above explanation of the operation of the control circuits for-the electric valves 25 and 25, it is apparent that the periods of conductivity of the electric valves 25 and 25 may be selectively predetermined, thereby to control the time interval for which the valve I8 is held in an open position by the solenoid I9. Thus, Where the tool head is a grinder such as shown in Figure 1, it is moved to a new position each time that the stock on the work table 6 completely passes the tool head Obviously, of course, where other tools are used in place of the grinder, the control arrangement may be modified so that the switch 2| is actuated only upon the movement of the work table 6 in a single direction rather than in both directions. Irrespective of the time or any variations thereof between successive closings of the switch 2|, the conductivity period for the valves 25 and 26 will always be the same. An arrangement such as shown and described has'been known to limit the possibilities of inaccuracy of operation since lthe control is accurate to 1/120 of a second or within the limits of a half cycle of alternating current. In one embodiment it was found that the tool head I! could be moved by any desired increments within an accuracy of 1/10,000 of an inch.

While for the purposes of illustrating and describing the invention, a particular circuit arrangement has been shown as applied to a particular machine tool, it, of course, is to be understood that I do not wish to be limited thereto, since obviously modiiications may be made in the circuit arrangement and in the apparatusto which the circuit may be applied Without departing from the spirit and scope of'my invention as set forth in the appended claims.

I claim:

1. An electric valve translating system comprising an alternating current source, a work circuit, a pair of reversely connected controlled electric valves interconnecting said sourceY and said work circuit, a control circuitV means for supplying to the control electrodes of lsaid valves an alternating current potential for biasing said valves non-conductive, means Vfor supplying to said circuit an alterna ig current potential of o-uc`n sign and magn 1 der ineective said biasing poten for connecting said means to said s rce for interval suiiicient to render conductive s said means thereupon being' energized no lsaid Work circuit, 'and means responsive to the initial-"-y tionof Aconductivity of said valves for determining'the' durationof conductivity oflsaid valves. -1 2. In an electric valve translating system hav-r ing a pair of reversely connected'controlled elec tric valves interconnecting an alternating current source and a work circuit, a control circuit including means energized from said source forV supplying to the control electrodes of said valves a potential for biasing said Valves non-conductive; means for supplying to said circuit an alternating potential vof such sign and magnitude as to render ineffective said biasing potential, means for energizing said rst means from said source for an intervalsufticient to render conductive said valves, said means thereupon being energized from said work circuit, and means respon-v sive to the initiation of conductivity of said valves for determining the duration of conductivity including an auxiliary valve'connected to reduce the potential supplied by said second means.

3. 'A control circuit for an electric valve translating system interconnecting an alternating current source'and a work circuit,`said system vincluding a pair of reversely connected controlled electric valves, saidV control circuit comprising means for supplyingV an alternating potential to bias said valves non-conductivey ar transformer for supplying an alternating potential of such sign and magnitude as to render ineiiective said biasing potential, means for energizing said transformer from said source for an interval sufcient to initiate conductivity of said Valves, said transformer being connected so that thereafter it is energized from said Work circuit, and means responsive to the initiation of conductivity of said'valves for determining the period of conductivity by controlling the potential supplied by said transformer.

f4. An electric valve translating system comprising a pair of reversely connected valves interconnecting an alternating'current source and a work circuit, a control circuit including means energized from said source for supplying an alternating current potential to bias said valves non-conductive, means for supplying a second alternating potential of such sign and magnitude as to render ineffective said biasing. potential, a switch for connecting said latter means to said source for an interval to render conductive said valves, and means responsive to the conductivity of said valves forreducing said second potential after a predetermined time of conductivity oiV said valves vto stop the conductivity thereof until Y said switch is again actuated.

5. A control circuit for an electric valve trans.- lating system having a pair of reversely connected Valves interconnecting an alternating current source and a work circuit, comprising means energized from said source'for supplying apotential to bias said valves non-conductive, a transformer for supplying a second alternating potential'of such sign and magnitude as to render ineiective said biasing potential, saidtransformer being connected so as to be energized in response to current owing in said work circuit, and means for energizing said transformer from said source for an interval sufcient to render conductive said valves. k Y Y "i 6. A control circuit for an electric valve translating system having a pair of reversely connected valves interconnecting an alternating current source and a work circuit7 comprising means energized from said source for supplying a poten--V tial to bias said valves non-conductive, a transformer for supplying a second alternating potential of such sign and magnitude as toA render ineiective said biasing potential, said transformer being connected so as to be energized in response to current flowing in said work circuit, means for energizing said transformer fromV said source for an interval sucient to render conductive said valves, and means responsive to the initiation of conductivity of said valves for determin-A ing the period during which said transformer is energized in response to current owing in said work circuit.

7. In an electric valve translating system having a Vpair of reversely connected controlled valves connected between a source of alternating current and a work circuit, a control circuit including a source of bias potential tending to maintain said valves non-conductive, means for supplying an alternating potential to maintain said valves conductive, means for connecting said rst means to said source for an interval sumcient to initiate conductivity of said valves, and circuit connections for causing said first means thereafter to be energized from said work circuit, and means operative after a predetermined .time interval after said initiation of -conductivity of said valves for shunting said rst means.

8. In an electric valve translating system having a pair of reversely connected controlled electric valves connected between a source of alternating potential and a work circuit, a control circuit including a source of bias potential tending to maintain said valves non-conductive, means for supplying an alternating'potential to maintain said valves conductive, a switch for connecting said means to said source for an interval suflicient to initiate Yconductivity of said valves, and circuit connections for causing said means thereafter to be energized from said work circuit, and auxiliary electric valve means operative after a predetermined time interval for shunting said rst means. i

9. In an electric valve translating system having a pair of reversely connected controlled electric valves interconnecting an alternating current source and a work circuit, a control circuit including a source of alternating bias potential tending to maintain said valves non-conductive, means for supplying an alternating potential to render said bias potential ineffective, a switch for connecting said means to said source for an interval suiiicient to initiate conductivity of said valves, and circuit connections for causing said means thereafter to be energized from said work circuit, and auxiliary electric valve means opera-` tive after a predetermined time interval after the initiation of conductivityV of said valves for shunting said first means, said auxiliary electric valve having a control electrode connected to an impedance arranged in parallel to a capacitor, said capacitor being connected so as to be charged by said source only during the non-conductive periods of said first valves.

10. In an electric valve translating system having a pair of reversely connected controlled electric valves interconnecting a work circuit and an alternating current source, means energized-from said source for supplying an alternating bias potential tending to maintain said Valves non-coni ductive, means forrsupplying second alternating potential of such sign and magnitude as to render` said first potential ineffective, a switch for connecting said second means to said source for an interval sulicientto initiate conductivity of said valves, circuit connections whichcausesaid second means thereafterto be Ienergized 'from said;

work circuit, and means responsive to the initiation of conductivity of said valves to determine the duration of conductivity, said means including an auxiliary control electric valve connected across said second means to reduce the potential supplied thereby, said auxiliary electric valve having a control electrode connected to an impedance arranged in parallel to a capacitor, and means for charging said capacitor only during the non-conductive periods of said rst valves.

11. In an electric valve translating system having a pair of reversely connected controlled elec-v tric valves interconnecting an alternating current source and a Work circuit, a control circuit including means energized from said source for supplying an alternating bias potential tending to maintain said valves non-conductive, a transformer for supplying an alternating potential of such sign and magnitude as to render said first potential ineffective, a switch for connecting said transformer to said source for an interval suincient to initiate conductivity of said Valves, said transformer being provided with connections so that thereafter said transformer will be ener gized from said work circuit, and means responsive to the initiation of conductivity of said valve to determine the duration of said conductivity including an auxiliary electric valve operative after a predetermined time interval to reduce the potential supplied by said transformer, said auxiliary electric valve having a control electrode connected to an impedance arranged in parallel to a capacitor, said capacitor being connected so as to be charged only during the non-conductive periods of said first valves by a rectifier connected to said source.

LEO F. LITTWIN. 

